Folks ,

I have a 1990 F-150 XLT 2WD 302 V8 , was driving the other day and started noticing the tach kept bottoming out at zero and then catch again. All of a sudden the truck stalled. Could not get it restarted. Had it towed home. Next day went out and it started right up , then after about minute started to have the same problem. The fuel pumps seems to be ok , because I have fuel pressure and I hear the pump make the correct noises that I would expect. I change the fuel filter however no luck. I check the Fuel pressure reg for fuel in the vaccum line and all is dry. Once truck has stalled it will not start again and I can smell fuel in the engine compartment , but no sign of any leaks. I have to wait a while before it will start and then do it's stall thing again. The check engine light does come on , however I thought I would ask here first before going out and buying a code scanner.

Any idea's

Thanks Mark

 

I'm not an expert by any means but the tach dropout would seem to suggest an ignition module or coil problem. There are ways to get the codes without having the tester but I cannot quote them as I have to look them up and my info is not with me. Search on this website as they are here somewhere.

 

Tach dropout means the coil is not firing, given how these trucks are wired. If she won't restart, watch the tach as you crank the engine . If the tach reads zero (or slightly above), the coil is not firing. (A normal engine reads about 300 rpm on the tach as you crank.) If you want to see this for yourself, while the truck is starting and running OK, pull the high voltage wire out of the coil, then try to start the truck. Watch the tach and you will see 200 to 400 RPM. Use this as a reference for the next time it breaks, and compare the difference.

Such a problem is limited to the TFI, pickup coil, ignition coil, ignition power circuits, and battery/frame grounds. You can pull the PCM (computer) clean out of the truck and you should still get spark and some reading on the tach as you crank.

When I had this intermittant problem, I thought it was a flaky TFI. (This is a very commonly reported issue). After replacing the TFI, the problem went away for a while, but came back. Replaced coil, distributor cap, rotor. The problem came back. It was very difficult to pin down the problem because the system kept "fixing itself".

Finally I cleaned up the chassis ground at the radiator support, and the battery ground cable. That fixed the problem.

To pull codes, go to fordfuelinjection.com and read the directions. But this action is not particularly indicated by these symptoms.

 

Thanks for the info , I'll try cleaning the ground as a first step. I do notice no rpm om the tach when cranking. I did notice when the it did start that the oil pressure was lower than it normally is , it did come up but that the truck stalled and would'nt start again so I could not determine what problem that might be. Could the oil pressure being low cause a no start ??

I have seen folks install a real aftermarket oil pressure gauge in combo with doing the stock oil pressure gauge fix with a Tee connector. Is it also possible to use the same approach with an aftermarket water temp gauge and the stock one , using a tee connector at the stock water temp gauge location

As soon as I get the starting issue found and fixed , I'll let ya know what it was.

Mark

 

The stock oil pressure guage is a glorified idiot light. It will either read "zero" or "mid scale". The sender is just a switch. There is a resistor in the guage cluster to fool the guage into reading mid-scale so long as the switch is closed. So if you have less than 7PSI the guage reads zero, more than 7PSI it reads mid-scale.

If the guage is reading something else (say 1/3 scale), then chances are the effective voltage to the instrument cluster is skewed from what it should be. This is a common symptom of a grounding problem.